Conventionally, in the case that variation occurs in inertia of a load which is a controlled object during operation of a motor, as an apparatus for identifying its inertia, for example, there is a control constant adjusting apparatus in Japanese Patent No. 3,185,857 proposed by the present applicant.
This apparatus includes a speed control part for determining a torque command so that an actual motor speed matches with a speed command inputted and controlling the motor speed, an estimation part for simulating the speed control part so that a speed of a model matches with the motor speed and an identification part for identifying inertia from a ratio between a value in which an absolute value of a value obtained by passing the torque command through a predetermined high-pass filter is integrated with respect to time at a predetermined interval and a value in which an absolute value of a value obtained by passing a model torque command of the estimation part through a predetermined high-pass filter is integrated with respect to time at the same interval, and is characterized in that the inertia is identified in the identification part only when the speed of the model in the estimation part matches with the motor speed in the speed control part at a value other than zero.
Since this apparatus can make identification in real time with respect to an arbitrary speed command, the identification can be made even when inertia of a load changes momentarily.
In the conventional control constant adjusting apparatus described above, when the speed control part is constructed by proportional integral control (hereinafter called PI control), constant disturbance such as gravity can be compensated by an integrator in the speed control part in a steady state, so that a speed deviation can be substituted for torque necessary to perform driving actually and there is no problem, but when the speed control part is constructed by integral proportional (hereinafter called IP control) control, a torque component necessary to perform driving actually cannot be separated from a torque component necessary to compensate disturbance, so that in this IP control, a problem that inertia cannot be identified arises.
Also, in the conventional control constant adjusting apparatus described above, the motor speed is set as a speed command of a model speed control part, so that there is a problem that delay in a model speed control system occurs and it takes time to reach identification since a model motor speed is difficult to match with the motor speed. Further, when there is load disturbance such as mechanical vibration or friction, the amount of compensation of the load disturbance is summed in a speed integral value in the actual speed control part, but it is difficult to reflect this amount of compensation of the load disturbance in a model. In the conventional art, processing for passing torque commands through the high-pass filter to sum the torque commands is performed, but there are cases where the high-pass filter does not work effectively depending on a frequency of disturbance and there is a problem that accuracy of identification becomes worse.